Controlled engine exhaust gas recirculation is a commonly used technique for reducing oxides of nitrogen in products of combustion that are exhausted from an internal combustion engine to atmosphere. A typical EGR system comprises an EGR valve that is controlled in accordance with engine operating conditions to regulate the amount of engine exhaust gas that is recirculated to the induction fuel-air flow entering the engine for combustion so as to limit the combustion temperature and hence reduce the formation of oxides of nitrogen.
Pintle-type EGR valves are commonly used, but the presence of the pintle within the valve passage restricts the area of the passage that is available to conduct the flow, and hence for a given flow, the passage diameter must be large enough to take the presence of the pintle into account. A butterfly-type valve offers certain advantages over a pintle-type, especially when applied to a diesel engine.
Various operating conditions that an EGR valve may encounter in a typical diesel engine include conditions where high flow rates must be conducted with minimal restriction and where large pressure differentials may appear across the EGR valve. A butterfly-type valve is capable of providing a low flow restriction operating condition, and it is less sensitive to pressure differentials acting across it because of its inherent force balancing character. However in order to take full advantage of a butterfly-type valve in a diesel engine application while satisfying all required operating conditions, a certain range of rotary motion is required. Ordinarily, a butterfly-type valve must be rotated substantially 90 degrees between full open and full closed positions in order to take advantage of its desirable characteristics. Such motion can be delivered to the valve by a linear actuator and linkage system, but the linkage system will typically add complexity and cost, and may even be disadvantageous in certain applications.
The present invention relates to new and unique embodiments of EGR valve that take advantage of the desirable attributes of a butterfly-type valve without the necessity of using a linkage system that provides 90 degrees of rotation for the valve. This makes the inventive EGR valve especially well-suited for use with a diesel engine, although broader principles of the invention are not necessarily limited to such specific engine usage.
An EGR valve must also be capable of withstanding the harsh operating environment where it is exposed to wide temperature extremes and corrosive elements. Since governmental laws and regulations are typically applicable to an automotive vehicle's engine EGR system, the EGR valve must also be capable of performing satisfactorily over the duration for which such laws and regulations are applicable to the vehicle's engine exhaust emission control system.
Since sealing of the butterfly-valve relative to the wall of the passage through the valve body when the valve is fully closed may at times be quite important, a sealing means may be required. Typically, such sealing means is disposed on the butterfly itself.
The present invention recognizes certain disadvantages of incorporating a sealing means on the butterfly, and instead comprises a sealing ring mounted in a groove in the wall of the passage. By placing the sealing ring on the wall of the passage, instead of on the butterfly, the mass of the butterfly can be minimized, thereby making for improved responsiveness of the butterfly to commanded changes in position. Certain machining operations on the butterfly are also avoided.
But mounting the sealing ring in a groove in the wall must be accomplished in such a way that the complications of mounting it on the butterfly are not merely transferred to mounting it on the valve body; especially to be avoided are complex machining and assembly operations.
In the inventive EGR valve, the groove is cooperatively defined by two axially end-to-end joined segments of the valve body for advantageous assembly of the various component parts. The sealing ring and butterfly are self-aligned during the assembly process, and the assembly process itself consists simply of fitting the two end-to-end segments of the valve body together to capture the sealing ring, and two associated parts, and concurrently ensure the alignment of the butterfly to the sealing ring.
The preferred forms of the inventive valve use aluminum or aluminum alloy for the valve body segments, and to minimize the possibility of galvanic action between the steel sealing ring and the aluminum valve body, respective stainless steel elements are placed to each side of the groove between the sealing ring and the valve body. One of these elements is resiliently sprung so that resilient axial force is applied to the sealing ring.
A rotary torque motor is also advantageously employed in the inventive valve in a unique geometric relationship, and the two segment construction of the valve body facilitates the incorporation of this feature into the inventive valve. With 45 degrees of rotation of its shaft, the torque motor accomplishes positioning of the butterfly from a fully closed position to a position of minimum restriction of the flow passage.
Further features, advantages, and benefits of the invention will be seen in the ensuing description and claims that are accompanied by drawings. The drawings disclose a presently preferred embodiment of the invention according to the best mode contemplated at this time for carrying out the invention.